A typical mechanism in a gun head for operating traditional grease gun pumps consists of a grease pressurizing ejection cylinder, with a piston slidably mounted within the cylinder, which reciprocates between a grease loading stroke and a grease pressurizing (ejection) stroke, back and forth across a grease inlet port in the gun head, which port is in communication with the grease pressurizing ejection cylinder in the head. The inlet port is also in communication with a metal barrel grease reservoir, which is removably affixed to the gun head, and may contain a grease cartridge positioned therein. Various typical pump constructions are show, for example, in U.S. Pat. Nos. 3,338,478; 3,344,084; 2,978,151; 1,368,840; 1,349,994; and 4,601,412, the disclosures of which are hereby incorporated herein by reference in their entireties.
In these mechanisms, grease is pressurized by a barrel piston with a compression spring within the barrel, and a barrel piston cocking rod. The compression spring, having one end bearing against the lower inner end of the barrel (not shown) and having its other end bearing against the lower end of the barrel piston within the metal barrel reservoir, urges the grease column within the reservoir, or cartridge within the reservoir, toward and through the inlet port and into the grease pressurizing ejection cylinder. The pump piston, located within the pressurizing ejection cylinder in the gun head, in the gun head closes off the inlet port on its pressurizing (ejection) stroke and forces the grease out of the gun head through a hose to a ZERK or equivalent fitting, and the pump piston opens the inlet port at the end of its suction stroke, loading the pressurizing ejection cylinder with grease urged by means of the compression spring. One-way valving opens the pressurizing ejection cylinder to the hose on the pump piston ejection stroke and closes off the cylinder to the hose on the pump piston suction stroke. Hand operated lever means or dual handle means operates the back and forth reciprocating action of the piston. One-way valving opens the pressurizing ejection cylinder to the hose on the pump piston ejection stroke and closes off the cylinder to the hose on the pump piston suction stroke.